As a former research geek in the radio business, I love telling 'the story behind the numbers'.
"Between 1993 and 2002, the share of Americans who said they were Protestant dropped from 63% to 52%, after years of remaining generally stable, according to a study released Tuesday by the National Opinion Research Center at the University of Chicago.
"At the same time, the number of people who said they had no religion rose from 9% to nearly 14%, and many are former Protestants, the survey's authors said."
"Among the reasons for the decline were the large number of young people and adults leaving denominations as the number of non-Protestant immigrants increased, comprising a greater share of the population. Also, a lower percentage are being raised Protestant...
This is not a positive change by any means.
"...it is also possible that some former Protestants are now identifying themselves only as 'Christian,' a choice on the survey."
That's bunk. Any Christian who isn't in communion with the Catholic church or Orthodox church is Protestant by definition and by default. "I'm just a Christian" means "I reject the trappings of an organized church" or "I just read/believe my Bible" which are both inherently Protestant approaches to Christianity.
"The Roman Catholic population has remained relatively stable over the period, making up about 25% of the U.S. population."
So what's really being said here is, Americans are increasingly frustrated spiritually, and neither the Catholics nor the Protestants have done a good job in reaching out (I'll stop short of saying "evangelizing").